Live Commentary: Victoria Azarenka vs. Simona Halep - as it happened

Good evening! There's just one place left in the semi-finals in the women's draw, with second seed Simona Halep and two-time finalist Victoria Azarenka preparing to head onto court to go head to head for that spot.

If you were following the first match on the Arthur Ashe court, you'll know that the winner of this match faces 26th seed Flavia Pennetta in the semis, after the Italian fought back from a set down against Petra Kvitova.

This will be just the third time that Azarenka has faced Halep. The Romanian has never beaten Azarenka, but they haven't faced each other since 2012. Since then, Halep has shot up the rankings, as she has been one of the most consistent players on the WTA tour over the last 18 months or so.

Azarenka has dropped just one set reaching the last eight, coming through her fourth-round match against American Varvara Lepchenko in straight sets. Halep had problems in the fourth round, struggling with a hamstring injury and complaining of dizziness after losing the opening set against Sabine Lisicki, before fighting back to progress. If she's still struggling with either of those issues today, it will play into Azarenka's hands.

The players have just walked out on court. Azarenka has complained of blistering on her arms as a result of her top. She wore bandages during her last match, but has gone with a slightly more elegant solution today, opting for compression sleeves like Nick Kyrgios and Milos Raonis wear to keep their serving arms warm.

While Azarenka reached the 2012 and 2013 finals in Flushing Meadows, Halep is in the quarter-finals for the first time, having only once been past the third round in New York before this year. She's had a disappointing run at the Grand Slams this year though, so will be keen to make amends at this tournament.

Right then, the players are ready to get the match underway, with Azarenka having won the toss and opted to receive first.

BREAK! Halep has her right thigh heavily strapped after struggling with an injury in her last match. At 30-30, Azarenka senses a chance to test her opponent's movement around the court, making an excellent forehand winner to the back corner to give her a chance for an early break, which she takes with a volley on the next point.

BREAK BACK! Halep's shows resolve early on as she quickly gets the set back on serve. Azarenka misses a couple of early serves, allowing Halep to attack on the return. The second seed creates to break points before she watches a backhand from the 20th seed go long, before another mistake from Azarenka hands her the game.

Azarenka is looking for another break as Halep makes a double fault, handing her opponent the lead, but a volley from the Belarusian goes long, before the second seed makes a stunning forehand followed by an ace. It's a confident finish to the game from the Romanian.

BREAK! Halep is making some brilliant returns, making a couple of flawless forehand winners to give herself a break point, but a change up in pace on the serve from Azarenka takes the game to deuce. The world number two picks out the sideline with another well-struck forehand to give herself another chance though, but this time slices her backhand into the net. A couple more chances for Halep to get the break come and go before a fifth break point is converted by the Romanian, with Azarenka forcing her forehand just long.

After a couple of closely-fought games, Halep wraps up a comfortable hold of serve, with Azarenka missing a string of returns before Halep hits another forehand winner. Azarenka has been trying to keep the ball away from Halep's backhand, but the second seed is playing some wonderful shots on the forehand side. Incidentally, in her two previous matches against Azarenka, Halep picked up just one game in three of her sets, and three in the other, so this is officially her best ever set against the former world number one.

Azarenka finds some powerful serves, forcing a run of three straight long returns from her opponent, but she misses her first serve while trying to clinch the game, allowing Halep to dictate the point from the back of the court and keep herself in the game, taking it to deuce on the next point when the 20th seed turns her forehand wide. Azarenka lets out a huge shout of "come on" as Halep fires long to give the Belarusian advantage, which she converts with another excellent serve. It looks like Azarenka is still trying to get herself pumped up for this match, but she's just about keeping herself in contention in the first set.

Halep is really racking up the winners in this opening sets, rifling a forehand down the sideline before slicing her backhand beyond Azarenka's reach. The 20th seed gets herself into a rally as she tries to extend the game, but she overhits a forehand, allowing Halep to hold serve.

Azarenka comes into the net to try to get herself going in this set, but double faults on the following point. She plays an excellent backhand on the next point, which the stretching second seed gets her racquet to, but can't get it back in play, while Halep misses her next return to give Azarenka the game. The Romanian will serve for the set next though.

SET! Halep is clearly a little nervous as she opens the game with a double fault, but she soon gets the game back on level terms with a forehand winner, which has been a valuable shot for her in this opening set. Her fastest serve of the match so far brings up set point, which she takes at the first time as asking as Azarenka hits her return long. It's the first time in her career that Halep has taken a set off the Belarusian.

Halep is waiting to get on with the second set, but Azarenka has gone off the court for a quick comfort break, so the world number two is sat waiting for her opponent to return.

Right then, Azarenka has returned from her break, and will serve first at the start of the second set.

Azarenka gets the opening point on the board with a nicely-struck volley, but Halep gets her into a rally, leveling the game with a backhand winner. A big serve from the 20th seed is followed up by a superb forehand down the line though, putting her 40-15 up. A double fault prolongs the game though, allowing Halep to take it to deuce with a backhand return right on the sideline. Halep misses her return though, allowing Azarenka to seal it with a couple of solid net shots.

BREAK! Halep produces some excellent defensive tennis behind the baseline, but a forehand on the stretch clips of the net before landing out. She dominates the next rally to unleash a winner, before sending down a big first serve. Superb! Azarenka displays the power she is famous for and comes to the court to finish the point with a stunning half volley. Break point arrives with a superb drive volley and Azarenka makes the breakthrough.

A challenge arrives from Halep early in the game, but the technology proves the Azarenka serve clipped the line. Halep is handed a point with a double fault, before sending a backhand long on the stretch. Azarenka secures the hold to 15 to stay ahead. Good response from the Belarussian.

Brilliant tennis throughout the game from Halep, who responds with a couple of superb forehands on the only occasions when the rally is extended. She will be determined to get back with serve now.

BREAK! Azarenka starts the game with a couple of big mistakes to open the door to Halep, who kicks it open by chasing down a poor drop shot to easily pass her rival with the passing forehand. Three break points. Azarenka saves one by going cross-court with a powerful forehand, but her serve is broken when Halep moves the 20th seed out wide before beating her down the line with a backhand winner. Key moment in the match.

BREAK! Azarenka regains some confidence with an unstoppable forehand winner to get to 15-15, but an attack of the second serve is wayward from the Belarusian moments later. It is the right tactic, though, and she capitalises on another weak serve before Halep goes long with a backhand. Azarenka should punish another second serve after taking control of the rally, but an unforced error from the back of the court leaves her frustrated. A superb forehand return winner gets Azarenka back to deuce, and a double fault brings up break point. Brilliant! Azarenka controls the point with some excellent ground strokes and delivers a fine drive volley before Halep drifts wide with the running backhand.

A passionate Halep attempts to get herself going again with a big celebration after a quite brilliant forehand winner. Azarenka hits back with a big serve/forehand combo, before edging ahead when Halep fails to find the line with the backhand. The Belarusian continues to struggle with the drop shot, and her poor execution is punished again as Halep shows her pace to beat her opponent with an excellent finish at the net. Azarenka powers back to secure the hold and she is a game away from the set.

Halep is under pressure when a couple of errors keep Azarenka at 30-30, but the Romanian does well to take charge of the next rally with a drop before finishing with an easy forehand into the open half of the court. Azarenka responds with a superb return of serve before displaying good footwork to force deuce with a forehand winner. Brilliant! A couple of big serves rescue Halep, who secures the hold by hammering do another forehand.

BREAK! Azarenka has a great chance to get to 30-0 when the court opens up for her, but she is a few inches wide with the forehand. Halep somehow manages to stay in the next point with returns off a couple of powerful volleys, before a delicate touch edges Azarenka ahead. Azarenka is then too short with a groundstroke, which allows Halep to unleash a winner with the forehand. 30-30. A break point arrives when Azarenka can only send back Halep's powerful backhand long. What a fightback. Halep rescues the second set when Azarenka finds the net. Can she now wrap up the match in straight sets?

SET! After serving for the set, Azarenka is gifted set point against the serve. Halep seems comfortable, before a double fault and a fine backhand winner from Azarenka gets her back in the game. It takes a couple of errors from Halep as she find the nets before going long to ruin her hard work. We are headed for a decider!

We are ready for more drama on Arthur Ashe, but the clouds are coming in and there is a few reports that the rain could start very soon. The problem could be if it starts, the rain may not stop tonight!

You would have expected the momentum to have shifted, but Azarenka creates an opportunity for her rival with a double fault. Halep finds the net with a slightly miscued forehand before the Romanian is handed two break points by an unforced error from Azarenka, who hits back to save one with some great length on her strokes before a brilliant forehand winner clinches the point. An excellent second serve down the middle allows her to retain the control and Halep is unable to find the line with the forehand on the run. Stunning! Point of the match as both players produce some fantastic shots from the baseline. The running is eventually too much for Halep, who is unable to get closer to Azarenka's superb forehand. A lack of patience prevents her from seeing out the game when she delivers a wayward forehand and an easy pass from Halep after chasing down yet another poor drop shot brings up a second break point. Azarenka bounces back with another winner, this time on the backhand side. A venture to the net ends with an emphatic volley from the Belarusian, but Halep refuses to give up! She gets behind a powerful stroke to beat the advancing Azarenka with a perfect backhand winner. Advantage is secured and lost once again from Azarenka, before a forehand winner edges her ahead when a Halep review proves she clipped baseline. The hold is finally clinched when Halep hits the net with a backhand. Azarenka somehow escapes a 10-minute game. It is turning into a memorable match in New York.

BREAK! Azarenka is furious on court as hawkeye does not arrive on the big screen, which leaves Halep waiting to serve once again. A few angry words are exchanged with the umpire, who does not know how to respond. It is good news for Azarenka when a couple of errors from Halep make it 0-30, but she hands a point back by finding the net with a forehand. Halep then gets level with a cleverly disguised forehand winner to wrong-foot her rival. Superb! Azarenka hammers a forehand down the line and Halep somehow gets a return back over the net, but the 20th seed shows her touch at the net with a brilliant half volley. Break! Halep goes long with the forehand and it is Azarenka is in front in the decider.

BREAK! Azarenka is left shocked when Halep delivers a superb backhand to clip the line, with a challenge prompting a second round of applause from the crowd. A chance arrives when Halep shows her class on the opposite side with a forehand winner as Azarenka moved a couple of steps in the other direction. Azarenka gets on the board in the game with a fine volley after reading the pass. However, a forehand into the net gifts break point to Halep, who is powerless to prevent her rival from hitting back with a powerful stroke that leaves her helpless behind the baseline. A second break point is secured when Halep gets on top of another short ball to produce a brilliant forehand to force the error from Azarenka, who gets level once again when the Romanian goes long on the stretch. Halep just will not go away. A seventh break point of the set for the second seed arrives with an Azarenka error, and another mistake sends a forehand into the net. What a match!

RAIN STOPS PLAY: Halep gets to 40-15 in her service game, but some light rain is falling. It was expected and the fear must be that the rain settles in now. The players have not left the court yet.

"It's only going to get heavier," a tournament official tells both players. Play has now been suspended and both Halep and Azarenka head off the court. It is unclear how long the delay will last, but the rain has certainly arrived earlier than most people expected.

Could a nightmare be about to take place at the US Open? Some people are suggesting that there could be some breaks in the rain, but heavy showers are expected this evening, tonight and tomorrow. Not good!

We'll take a break from the live text coverage as the players look set to be off for an extended spell. Make sure all of you are keeping your fingers crossed and let's hope for more from these two soon!

Welcome back everyone! The rain has gone, for now, and play is almost ready to resume on Arthur Ashe as Halep looks to stay with serve in the deciding set. Azarenka currently leads 2-1, but Halep is 40-15 ahead in the third game.

As a result of the rain, Stan Wawrinka vs. Kevin Anderson has been moved to the Louis Armstrong Stadium and should get underway at around 11pm (BST).

Will this break affect the match? It was a thrilling encounter before the interval, but one or both players may struggle to find their rhythm after waiting in the locker room.

Perfect from Halep. She returns with an ace to hold her serve.

Azarenka is forced to wait for one particularly slow spectator, but she starts the game impressively by following a big first serve with a forehand winner. Another powerful forehand follows, before the drive volley moves her further ahead. Halep has the chance to put away a forehand in the next rally, but she pays for the hesitation as Azarenka moves forward to execute the perfect drop volley. A double fault halts the 20th seed, who recovers to take the game with the next point.

The deciding set continues with another comfortable hold as Halep delights the crowd by clipping the line with a stunning backhand down the line. Azarenka manages to punish a second serve with a powerful winner, but another backhand follows from the second seed as Halep holds to 15.

BREAK! Halep goes shot-for-shot with her rival from the baseline and, surprisingly, beats her for power to get to 15-15 early in the game. A couple of superb strokes from Azarenka move her back ahead as she sends Halep wide before going in the opposite direction with the winner. Halep is then too good with the return of a second serve, and the angle of the follow-up forehand is perfect as she pulls level again. A fine rally brings the best out of both players, but Halep blinks first by going wide with a forehand on the stretch. Halep hits back with some brilliant forehands and a winner is followed by a big fist pump from the Romanian. Azarenka delivers a double fault at the worst possible time to hand break point to Halep, who wastes the opportunity by sending a miscued backhand wide. An unforced error brings up a second break point and Halep capitalises when Azarenka finishes a long rally by going with wide with the backhand. Huge moment in the match. Can Halep hold her nerve?

Halep has second thoughts about a challenge when Azarenka finds the line with an unstoppable forehand, and hopes of a response from the Belarusian are raised when she watches her rival send a forehand of her own wide. The second seed hits back with a winner before Azarenka finds the net to make it 30-30. A couple of superb ground strokes from Halep hit the perfect length and Azarenka is unable to keep her response from drifting long. However, a second serve is just far too inviting for Azarenka to turn down as she delivers a return winner to get to deuce. Halep edges ahead when her fastest serve of the match is sent back at the net. Azarenka gets another second serve to attack, but she hits the backhand wide and Halep is one game away from the semi-finals.

The Azarenka challenge starts to fade at the start of the game as two errors open the door to Halep, who is powerless to prevent the Belarusian from hitting back with a volley after moving her from side to side. Halep's forehand then goes long, before Azarenka moves to game point with a fantastic backhand winner. Great response from the former world number one. She wraps up the game to ensure that Halep must finish the job on her serve.

GAME, SET AND MATCH! Brilliant from Halep. With all of the pressure on her shoulders, the second seed holds her nerve. Azarenka gets forward early in the game to make it 15-15 with an unstoppable forehand, before Halep uncharacteristically misses with a good opportunity on the backhand. A forehand into the net stops Azarenka from bringing up two break points. Halep delivers when it matters with a forehand winner to bring up match point, before Azarenka goes wide with a forehand of her own to bring a thrilling match to an end!

What a match on Arthur Ashe. After a long rain delay interrupted an incredible contest, it was Halep who produced the big shots when play resumed to clinch the win which sends her through to a first US Open semi-final.

The women's semi-finals are now decided. Halep's reward for victory is a meeting with Flavia Pennetta, while world number one Serena Williams continues her bid for a clean sweep of the Grand Slams against the unseeded Roberta Vinci.

That's all from our live coverage of the match, but make sure you keep an eye out for text commentary of Roger Federer vs. Richard Gasquet from 12am (BST). Goodnight everyone.